1. Field of the Invention
This invention relates to optical data reproducing devices for video disks or digital audio disks.
2. Discussion of Prior Art
A first conventional optical data reproducing device is shown in FIGS. 1 through 3. In these figures, reference numeral 1 designates a light source such as a semiconductor laser. A laser beam from the semiconductor laser 1 is converted into a parallel beam by a collimator lens 2. The parallel beam is split into three beams by a diffraction grating 3. The beams are passed through a polarization beam splitter 4 which is sometimes referred to hereafter as a separating optical system. The beams are then converted into circularly polarized beams by a quarter-wave plate 5 and then applied to an objective 6. As a result, beams 10a, 10b and 10c are focused on pits 7a of an optical disk 7. The collimator lens 2, diffraction grating 3, quarterwave plate 5 and objective 6 of the optical system are sometimes referred to hereafter as a focusing optical system. The beams 10a, 10b and 10c are reflected by optical disk 7. The beams thus reflected, namely, read beams 12a, 12b and 12c, advancing along the optical path in the direction opposite to the direction in which the beams 10a, 10b and 10c are applied to optical disk 7, reach quarter-wave plate 5 through objective 6 where they are converted into linearly polarized beams. Since the linearly polarized beams are per endicular to the incident beams, they are reflected by polarization beam splitter 4. The beams thus reflected are applied through a focus detecting optical system 8 to a photo-electric conversion element 9. The photo-electric conversion element, as shown in FIG. 3, has three light receiving surfaces 9a, 9b and 9c where the middle light receiving surface 9b is divided into four parts. The read beams 12a, 12b and 12c are applied to the light receiving surfaces 9a, 9b and 9c, respectively. The optical signals are converted into electrical signals by the photo-electric conversion element 9. The difference between the outputs of the light receiving surfaces 9a and 9c is outputted, as a track error signal (hereinafter referred to as "a TE signal", when applicable), by a subtractor 13. The difference between the outputs of the diagonally opposite parts of the middle light receiving surface 9b (which is divided into four parts as described before) is outputted, as a focus error signal (hereinafter referred to as "an FE signal", when applicable), by a subtractor 14. On the other hand, the sum of the outputs of the four division parts of the light receiving surface 9b is outputted, as a reproduction signal (hereinafter referred to as "an RF signal", when applicable), by an adder 15. The output terminals of the subtractors 13 and 14 are connected to tracking and focus servo circuits (not shown). The outputs of these circuits operate an actuator, to perform tracking and focus servo operations. The output terminal of the adder 15 is connected to a signal processing circuit (not shown) which reproduces the data on the optical disk 7.
In the conventional optical data reproducing device, the light beam from the light source is split into three beams 10a, 10b and 10c by the diffraction grating 3 and the three beams are applied onto one track as shown in FIG. 2. Therefore, whenever a trick play jump is desired, it is necessary to apply the beams 10a, 10b and 10c to a different track, for instance, by moving the device itself radially of the optical disk 7. Accordingly, the speed of the trick play is limited to some degree. Moreover, it is impossible for the device to reproduce data on different tracks simultaneously.
In view of the foregoing, an object of this invention is to provide an optical data reproducing device in which a trick play jump can be performed instantaneously, the speed of the trick play can be increased, and data on different tracks can be reproduced simultaneously.
The foregoing object and other objects of the invention have been achieved in one detailed embodiment of the invention by the provision of an optical data reproducing device which comprises: a light source; a focusing optical system for focusing light beams from a light source onto an optical disk; a separating optical system provided on the optical path of the focusing optical system for separating light beams, which are reflected as optical signals from the optical disk, from the optical path; a photo-electric conversion element for receiving the light beams, which are separated from the optical path by the separating optical system, to convert the optical signals into electrical signals; and a circuit for processing the electrical signals from the photo-electric conversion element to perform data reproduction and various servo controls, the focusing optical system having a plurality of diffraction gratings which have at least two optical grating surfaces, the grating directions of which are substantially perpendicular to each other, the diffraction gratings being adapted to apply three light beams to each of at least two tracks on the optical disk and being disposed between the light source and the separating optical system and the photo-electric conversion element having at least two light receiving sections for receiving light beams reflected from the tracks.
Another conventional optical data reproducing device is shown in FIGS. 4 through 6 where common reference numerals in the figures refer to like parts. The parallel beam from collimator lens 2 is applied through polarization beam splitter 4 to quarter-wave plate 5, where it is converted into a circularly polarized beam. The beam is focused, as a beam 10, on a pit 7a a on optical disk 7 by an objective 6 as shown in FIG. 5. The assembly of the collimator lens 2, quarter-wave plate 5 and objective 6 may sometimes be referred to as "a focusing optical system". The beam reflected by optical disk 7 namely, a read beam 12, advancing along the optical path in the direction opposite to the direction in which the beam has advanced to the optical disk, reaches quarter-wave plate 5 through objective 6, so that it is converted into a linearly polarized beam. Since the linearly polarized beam is perpendicular to the incident beam, it is reflected by polarization beam splitter 4. The beam thus reflected is applied through focus detecting optical system 8 to photo-electric conversion element 9.
The photo-electric conversion element 9 has a four-division light receiving surface 11 consisting of four division surfaces 11a, 11b, 11c and 11d. The read signal 12 is applied to the four-division light receiving surface 11. As a result, a track error or TE signal, a focus error or FE signal and a data reproduction or RF signal are detected by a signal detecting circuit 25 connected to photo- electric conversion element 9. More specifically, in the division surfaces 11a and 11c, the optical signals are converted into electrical signals. The electrical signals outputted by division surfaces 11a and 11c are subjected to addition in a first adder 16. Electrical signals outputted by division surfaces 11b and 11d are subjected to addition in a second adder 17. The outputs of the two adders 16 and 17 are subjected to subtraction in a subtractor 18, so that the FE signal is provided at an output terminal 19. The sum of the outputs of all the division surfaces 11a through 11d is calculated by a third adder 20, so that the RF signal is provided at an output terminal 21. The sum of the outputs is subjected to time differentiation in a differentiation circuit 22. The output of the differentiation circuit 22 and the output of the subtractor 18 (which is the difference between the sum of the outputs of the division surfaces 11a and 11c and the sum of the outputs of the division surfaces 11b and 11d ) are subjected to multiplication in a multiplier 23, so that the TE signal is provided at an output terminal 24.
The output terminals 19 and 24 are connected to a focus servo circuit and a tracking servo circuit (not shown). The outputs of these circuits operate an actuator, to perform the tracking servo control and the focus servo control. The output terminal 21 is connected to a signal processing circuit (not shown), to reproduce data on the optical disk 7.
In the above conventional optical data reproducing device, the beam 10 is applied to one track. Therefore, whenever a trick play jump is desired, it is necessary, for instance, to move the device itself radially of the optical disk 7 to cause the beam 10 to irradiate another track. Accordingly, the speed of the trick play is limited to some degree. Moreover, it is impossible for the device to reproduce the data of different tracks simultaneously. Thus, the prior art device of FIGS. 4 through 6 is subject to the same shortcomings as those of the device of FIGS. 1 through 3.
The above shortcomings have also been overcome in another detailed embodiment of the invention comprising: a light source; a focusing optical system for focusing light beams from the light source onto an optical disk, a separating optical system provided on the optical path of the focusing optical system for separating light beams from the optical path which are reflected as optical signals from the optical disk; a focus detecting optical system for receiving the reflected beams which are separated by the separating optical system to detect light beam focusing conditions on the optical disk; a photo-electric conversion element for receiving the reflected beams which have passed through the focus detecting optical system to convert the optical signals into electrical signals; and a circuit for processing the electrical signals from the photo-electric conversion element to perform data reproduction and various servo controls, the focusing optical system having a diffraction grating adapted to split a light beam from the light source into at least two beams which are projected onto two tracks on the optical disk, respectively and the diffraction grating being disposed between the light source and the separating optical system, the photoelectric conversion element including at least two light receiving sections which receive the light beams reflected from the tracks, respectively, the light receiving sections each having a four-division light receiving surface.